The present invention relates to devices for the fixation and/or support of bones. In particular, the present invention relates to a bone support assembly, and a corresponding bone support plate, for the fixation and/or support of bones of the spinal column. The plate of the present invention has particular application in situations where compressional or xe2x80x9csettlingxe2x80x9d forces, as well as torsional and flexing forces, of xe2x80x9cfixedxe2x80x9d vertebrae on a spinal plate cause significant stressing and potential failure of the spinal plate and/or plate components.
Vertebral fixation has become a common approach to treating spinal disorders, fractures, and for fusion of vertebrae at the time such fixation is instituted. Namely, one or more vertebrae are fixed in position relative to one or more other vertebrae above and/or below the vertebrae to be fixed. Generally, a spinal plate is the device of choice used for mechanically supporting such vertebral fixation. A typical spinal plate includes a plate having a plurality of apertures therethrough. A corresponding plurality of fasteners, i.e., bone screws, are generally positioned into and through respective apertures of the plate to secure the spinal plate to a bone, such as two respective upper and lower supporting adjacent spinal vertebrae. The screws are fastened to the respective support vertebrae to secure the spinal plate to the respective vertebrae. In general, such plate and screw assemblies can be utilized, generally, for anterior fixation of the spine for cervical, lumbar, and/or thoracic fixation.
The basis of anterior fixation or plating is to approach the spine from an anterior or anterio-lateral approach, and use the screws to solidly mount the spinal plate to the affected vertebrae. Often, in addition to the application of a spinal plate, graft material may be combined in an attempt to permanently fuse together adjacent vertebrae. The graft material can consist of bone grafts obtained from bones of the recipient or another individual.
A common problem associated with the use of such spinal plates is the tendency of the bone screws to xe2x80x9cback outxe2x80x9d or pull away or withdraw from the bone into which they are fixed. This problem occurs, primarily, due to the normal torsional and bending motions of the body and spine. This is a particularly important problem because as the screws become loose and pull away or withdraw from the bone, the heads of the screws can rise above the surface of the spinal plate and, possibly, even work their way completely out of the bone. While this condition can cause extreme discomfort for the recipient, this condition can also create a number of potentially serious physiological problems given the significant amount of nervous and vascular structures associated at or near the potential locations of anterior spinal plate fixations.
A number of designs have been proposed in attempts to prevent screws from pulling away or withdrawing from the bone and/or to prevent the screws from backing out or pulling away or withdrawing from the surface of the spinal plate. Such mechanisms used to prevent bone screws from pulling out of bones include cams which engage and lock the screws, and the use of expanding head screws which expand outwardly when adequate force is applied thereto to engage the holes in the spinal plate. All of these designs have detriments including potential for breakage or requiring particular precision and alignment in their application in order to work correctly. Additionally, loose components and accessories of spinal plates which address the xe2x80x9cbacking-outxe2x80x9d or withdrawal problem can get dropped and/or misplaced while the vertebral fixation surgical procedure is taking place, prolonging and complicating the procedure as well as creating substantial risk of harm to the recipient.
Yet another common problem associated with the use of such spinal plates is the tendency of the vertebrae being xe2x80x9cfixedxe2x80x9d to settle after spinal plate insertion adding compression forces to the above-listed forces which cause the bone screws to xe2x80x9cback outxe2x80x9d or pull away or withdraw from the bone into which they were fixed.
It is an object of the invention to provide bone support assemblies which provide rigid bone-to-bone fixation and/or support, such as e.g. adjacent or second adjacent vertebrae, while allowing post-procedural compression between the respective bones.
It is another object of the invention to provide bone support assemblies which afford substantial protection against pulling away or withdrawal of affixing components which may result from torsional movement, flexing movement, or stress and/or dynamic load sharing of the vertebrae, thereby enhancing the bone rebuilding process.
It is yet another object of the invention to provide bone support assemblies which attenuate application of stress on the apparatus and affixing components
It is a further object of the invention to provide bone support assemblies comprising a bone support plate and resiliently flexible bands so mounted and positioned to enable bone fasteners to pass such bands when being installed in a recipient and which prevent withdrawal of such bone fasteners after installation in the recipient.
It is yet a further object of the invention to provide bone support assemblies which can be completely pre-assembled such that no assembly steps need be performed on the bone support assembly during installation of such bone support assembly in a recipient thereof.
It is still a further object of the invention to provide bone support assemblies wherein apparatus, in such bone support assemblies, for preventing withdrawal of bone fasteners from the bone, after installation on a recipient, are automatically activated, to prevent such withdrawal, as a consequence of the installation of the bone fasteners.
This invention provides a novel bone support assembly, and methods of use, wherein a locking member such as a resiliently flexible band, mounted to the bone support plate, automatically and as a consequence of driving a bone fastener through the bone support assembly and into bone structure of a recipient of such bone support assembly, activates a locking feature of the bone support assembly to thereby prevent the bone fastener from withdrawing out of the bone support assembly and past the locking member.
Thus, the invention comprehends a bone support assembly, comprising a bone support plate. The bone support plate comprises a top surface, a bottom surface opposite the top surface and adapted to engage bone structure of a recipient, a plurality of bone-fastener-receiving apertures for receiving bone fasteners therethrough for securing the bone support assembly to the bone structure of the recipient. The bone support assembly further comprises a locking member mounted to the bone support plate, the locking member being effective, when a bone fastener is driven through an aperture into bone structure of a recipient, to automatically and as a consequence of driving the bone fastener, activate a locking feature of the bone support assembly effective to prevent the bone fastener from withdrawing out of the bone support assembly and past the locking member.
In preferred embodiments, the locking member comprises a resiliently flexible band. A length of the band extends along a side of one or more corresponding ones of the apertures whereby, as the bone fastener is driven, a break structure of the bone fastener, such as a screw head, can urge the band to automatically flex transversely of the length of the band, from a first flexural condition, until the break structure in the bone fastener is driven past the band, whereupon the band returns to the previous flexural condition and overlies the break structure of the so-driven bone fastener and thereby prevents the bone fastener from withdrawing.
Also in preferred embodiments, the bone support plate further comprises a channel defined in and as part of the top surface of the bone support plate. The channel has side walls opening into and extending alongside ones of the plurality of bone-fastener-receiving apertures. The resiliently flexible band is disposed in the channel and extends along a side of the channel.
The channel preferably has a bottom surface.
In some embodiments, at least all except two of the bone-fastener-receiving apertures comprise slots, enabling longitudinal movement of bone fasteners in the slots, with respect to the bone support plate, and first and second ones of the bone-fastener-receiving apertures can comprise circular openings.
In preferred embodiments, all of the bone-fastener-receiving apertures comprise slots, having lengths greater than respective widths of the slots.
Preferably, the flexible band extends along substantially a full length of the bone support plate.
The bone support assembly preferably includes a second flexible band and the first and second flexible bands extend along substantially full lengths of respective first and second sides of the channel, the first and second flexible bands collectively extending along the sides of all of the bone-fastener-receiving apertures.
The bone support assemblies preferably comprise one or more band retainers mounted to the bone support plate, and mounting the flexible band to the bone support plate.
In some embodiments, the band retainers mount the bands to the plate with abutment of the retainer against the flexible bands and urging of the flexible bands against respective first and second sides of the channel through such abutment.
In other embodiments, a retainer comprises a stud extending through the retainer-receiving aperture, the stud being welded to the bone support plate adjacent the bottom surface of the bone support plate.
Compositions of the flexible band preferably comprise predominantly nickel and titanium. Preferred compositions of the flexible bands comprise about 55 percent by weight to about 56 percent by weight nickel and about 44 percent by weight to about 45 percent by weight titanium.
The compositions of flexible bands of the invention preferably comprise shape memory metal alloys, which can be predominantly nickel and titanium, although other materials can be used so long as the material has the requisite flexural properties, has suitable strength properties, and is safe for use in living body surgical procedures.
In preferred embodiments, the bone support plate is elongated. The bone-fastener-receiving apertures are arrayed in first and second rows along a length of the bone support plate. The bone support assembly further comprises a second resiliently flexible band, and the first and second bands are mounted at the opposing side walls of the channel, and extend along a portion of the length of the channel occupied by the bone screw apertures.
In preferred embodiments, first and second bands are mounted to the bone support plate by at least one band retainer, preferably a plurality of band retainers, displaced from the apertures, and the first and second bands can flex at respective slots about mounting loci displaced longitudinally along the bone support plate from respective ones of the bone screw apertures, when bone screws are driven through the bone support plate and respectively past respective edges of the bands.
The invention further comprises a method of mounting a bone support to bone structure. The method comprises providing a bone support assembly, comprising a bone support plate, having a top surface, a bottom surface opposite the top surface and adapted to engage bone structure of a recipient, and a plurality of bone-fastener-receiving apertures for receiving bone fasteners therethrough for securing the bone support assembly to such bone structure of such recipient, and one or more resiliently flexible bands mounted to the bone support plate, a length of the band extending along sides of corresponding ones of the apertures. The method further comprises driving a bone fastener through a respective bone-fastener-receiving aperture and including driving a break structure of the bone fastener past the flexible band such that the break structure of the fastener causes the flexible band to flex transversely of the length of the band, from an unflexed condition, as the break structure of the bone fastener passes the band whereupon, when the break structure of the fastener moves past the flexible band, the resiliently flexible band returns to the unflexed condition and overlies the break structure of the so-driven bone fastener, thereby preventing the bone fastener from withdrawing out of the bone support assembly past the resiliently flexible band.
In preferred embodiments, the method includes driving a plurality of bone fasteners through respective bone-fastener-receiving apertures in the bone support plate, including driving each bone fastener a sufficient distance toward the bone support plate that a break structure on the respective fastener passes the flexible band whereby the flexible band flexes over the break surface of the fastener and thereby prevents the bone fastener from withdrawing out of the bone support assembly past the resiliently flexible band.